In continuously extruded blow-molding processes, a hollow tube of melted polymer, or “parison,” is typically extruded through an annular die and into a moving mold. As the parison enters the moving mold, the parison is expanded with pressurized air or gas to force the parison into the shape of the mold. In some cases, a vacuum is also applied to the cavity within the mold to draw the parison against the interior walls of the mold. As the molten parison takes the hollow shape of the mold, and travels with the mold away from the hot extruder, the mold, the polymer, and any air or gas within the hollow center of the molded polymer begins to cool.
Variations of such continuous extrusion blow-molding processes may be used to manufacture corrugated polymer pipe. For example, corrugated polymer drainage pipe may be co-extruded from molten polyethylene and/or polypropylene and blow-molded into a desired profile. One method of manufacturing polymer pipe involves co-extruding a smooth inner layer and a corrugated outer layer of pipe into moving molds of a corrugator. The two layers of polymer are generally extruded at a temperature sufficiently high to allow them to conform to the inner corrugated cavity of the mold and properly bond with each other, as desired, depending on the particular composition of polymer. Specifically, the extruded layers of polymer are extruded at a temperature hot enough to melt both layers of the polymer, such that polymer chains of the two layers intersperse and then cool together. This results in the smooth inner wall and the corrugated wall being integrally fused or bonded together wherever they contact each other.
When manufacturing large diameter corrugated pipe, the extruded polymer layers may be disposed inside the molds of a corrugator or vacuum chamber for a period of time (i.e., “residence time”) during which a substantial amount of cooling is desired. Specifically, the layers of polymer are desired to be cooled to a temperature at which they are no longer susceptible to substantial deformation, even when the molds of the corrugator are opened. Previous attempts at cooling the molds of a corrugator have been complicated, unreliable, and, in some cases, have interfered with vacuum mechanisms used to blow-mold the polymer layers into the mold cavities. Moreover, previous attempts at cooling the molds have been unable to efficiently provide a sufficient level of heat transfer to cool the mold housing, mold cavity, and polymer therein to an acceptable temperature. In some instances, these limitations have constrained the rate at which products are manufactured.
Accordingly, there is a need for systems and methods for cooling moving molds used in manufacturing corrugated polymer pipe.